Re: [PATCH v3 3/5] cpufreq: report whether cpufreq supports Frequency Invariance (FI)

[Viresh Kumar]

On 24-08-20, 22:02, Ionela Voinescu wrote:
> Now that the update of the FI scale factor is done in cpufreq core for
> selected functions - target(), target_index() and fast_switch(),
> we can provide feedback to the task scheduler and architecture code
> on whether cpufreq supports FI.
> 
> For this purpose provide an external function to expose whether the
> cpufreq drivers support FI, by using a static key.
> 
> The logic behind the enablement of cpufreq-based invariance is as
> follows:
>  - cpufreq-based invariance is disabled by default
>  - cpufreq-based invariance is enabled if any of the callbacks
>    above is implemented while the unsupported setpolicy() is not
> 
> The cpufreq_supports_freq_invariance() function only returns whether
> cpufreq is instrumented with the arch_set_freq_scale() calls that
> result in support for frequency invariance. Due to the lack of knowledge
> on whether the implementation of arch_set_freq_scale() actually results
> in the setting of a scale factor based on cpufreq information, it is up
> to the architecture code to ensure the setting and provision of the
> scale factor to the scheduler.
> 
> Signed-off-by: Ionela Voinescu <ionela.voinescu@xxxxxxx>
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
>  drivers/cpufreq/cpufreq.c | 20 ++++++++++++++++++++
>  include/linux/cpufreq.h   |  5 +++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 34533c6b3bd0..b3a7d1cc5e92 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -61,6 +61,9 @@ static struct cpufreq_driver *cpufreq_driver;
>  static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
>  static DEFINE_RWLOCK(cpufreq_driver_lock);
>  
> +/* Mark support for the scheduler's frequency invariance engine */
> +static DEFINE_STATIC_KEY_FALSE(cpufreq_freq_invariance);
> +
>  /* Flag to suspend/resume CPUFreq governors */
>  static bool cpufreq_suspended;
>  
> @@ -69,6 +72,20 @@ static inline bool has_target(void)
>  	return cpufreq_driver->target_index || cpufreq_driver->target;
>  }
>  
> +static inline
> +void enable_cpufreq_freq_invariance(struct cpufreq_driver *driver)
> +{
> +	if (!driver->setpolicy) {
> +		static_branch_enable_cpuslocked(&cpufreq_freq_invariance);
> +		pr_debug("supports frequency invariance");
> +	}
> +}
> +

I would rather open-code this int the cpufreq_register_driver() routine as
that's what is done in cpufreq_unregister_driver() as well.

> +bool cpufreq_supports_freq_invariance(void)
> +{
> +	return static_branch_likely(&cpufreq_freq_invariance);
> +}
> +

And would keep the definition of the static key with this routine at a single
place.

>  /* internal prototypes */
>  static unsigned int __cpufreq_get(struct cpufreq_policy *policy);
>  static int cpufreq_init_governor(struct cpufreq_policy *policy);
> @@ -2721,6 +2738,8 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
>  	cpufreq_driver = driver_data;
>  	write_unlock_irqrestore(&cpufreq_driver_lock, flags);
>  
> +	enable_cpufreq_freq_invariance(cpufreq_driver);
> +
>  	if (driver_data->setpolicy)
>  		driver_data->flags |= CPUFREQ_CONST_LOOPS;
>  
> @@ -2790,6 +2809,7 @@ int cpufreq_unregister_driver(struct cpufreq_driver *driver)
>  	cpus_read_lock();
>  	subsys_interface_unregister(&cpufreq_interface);
>  	remove_boost_sysfs_file();
> +	static_branch_disable_cpuslocked(&cpufreq_freq_invariance);
>  	cpuhp_remove_state_nocalls_cpuslocked(hp_online);
>  
>  	write_lock_irqsave(&cpufreq_driver_lock, flags);
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index 8f141d4c859c..091df9968945 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -217,6 +217,7 @@ void refresh_frequency_limits(struct cpufreq_policy *policy);
>  void cpufreq_update_policy(unsigned int cpu);
>  void cpufreq_update_limits(unsigned int cpu);
>  bool have_governor_per_policy(void);
> +bool cpufreq_supports_freq_invariance(void);
>  struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy);
>  void cpufreq_enable_fast_switch(struct cpufreq_policy *policy);
>  void cpufreq_disable_fast_switch(struct cpufreq_policy *policy);
> @@ -237,6 +238,10 @@ static inline unsigned int cpufreq_get_hw_max_freq(unsigned int cpu)
>  {
>  	return 0;
>  }
> +static inline bool cpufreq_supports_freq_invariance(void)
> +{
> +	return false;
> +}
>  static inline void disable_cpufreq(void) { }
>  #endif
>  
> -- 
> 2.17.1

-- 
viresh